I need help understanding how an n-fet works i have chosen one ( irf520) it can handel alot of power about 10 amp or so, but why is it getting so hot when it is only handling a load of 1.0 amp?
I have mounted it on a large heat sink because i want to make a salt water one day and i may then nead 6amp pr. Channel!!
But how hot vil it be at that load ?

Is it becurse i have a resistor betwin Arduino pin 9 and gaten on the fet so it dosent open totely?? Is it nessasery with a resistor?